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silver darling
silver darling
Known Participant
November 5, 2017
Answered

PS increases digital file size (kb , mb) ?

  • November 5, 2017
  • 1 reply
  • 8754 views

Excuse basic question. I'm seeking clarity on file sizes in photoshop. The digital file size, in KB or MB. I need to optimise images for web delivery. All I want to do is open an image and reduce file size by reducing quality.

If I open an image in PS (CC) that multiple apps in windows tell me is 250 kb file size, PS tells me the image is much larger. What is going on?

Example -

File size via windows -

Same file via filezilla

At this point I believe image to be c. 280 kb .

Open same image in PS and PS tells me -

'Document size' is 4.12M

This 'M' I understand to be size of paper required to print image. Where can I see the info that tells me the file size of the image in kb?  Adobe 'help' pages say -

"You can view the file size information for an image at the bottom of the application window."  - Photoshop image size and resolution and that article refers to digital (file) sizes. But this appears to be fantasy.

To reduce size I select File > Export > Export as .  PS reports the image to be 765.1 kb

Somehow the image has tripled in file size even though I made no changes to image. Exported with no changes it's 750kb -

The legacy 'export for web' does the same. Reducing image quality via 'export as' to get back to the original file size gives very poor quality , much worse than the original image.

Surely this is basic workflow, why is PS increasing the file size? What basic insight am I missing here?

Any clarification would be much appreciated. thanks.

This topic has been closed for replies.
Correct answer gener7

Where to start:

There are two ways of describing file sizes: Decimal and Binary  279 KB Decimal x 1.024 = 285,696 bytes Binary. Same size different notation.

Jpeg is a compressed format for storing on drives.  The 4.12M is Megabytes as the size in memory opened in Photoshop. It is not a print unit.

Use File > Export > Save for Web. There you can adjust to the compressed size you want while seeing how the image looks.

You can also opt to set Metadata to None and even reduce pixel dimensions. Reducing quality to crunch down the file size means losing detail to do that.

Ok, I'll let you absorb that and return if you have questions.

Gene

1 reply

gener7
Community Expert
gener7Community ExpertCorrect answer
Community Expert
November 5, 2017

Where to start:

There are two ways of describing file sizes: Decimal and Binary  279 KB Decimal x 1.024 = 285,696 bytes Binary. Same size different notation.

Jpeg is a compressed format for storing on drives.  The 4.12M is Megabytes as the size in memory opened in Photoshop. It is not a print unit.

Use File > Export > Save for Web. There you can adjust to the compressed size you want while seeing how the image looks.

You can also opt to set Metadata to None and even reduce pixel dimensions. Reducing quality to crunch down the file size means losing detail to do that.

Ok, I'll let you absorb that and return if you have questions.

Gene

silver darling
silver darlingAuthor
Known Participant
November 5, 2017

Gene thanks for this - 'The 4.12M is Megabytes as the size in memory opened in Photoshop' that is useful info.  But with respect i do understand kb sizes.

The issue is that a file sized at 270kb, or c. 270,000 bytes whichever you prefer , auto converts to 750kb when using file>export dialogue in PS. Which bytes conversion equation is PS using for that? Using legacy save for web produces same results. Also I cannot see a way to simply view digital filesize in PS. 

If you read my question and look at the screen shots you may understand the issue better.

gener7
Community Expert
gener7Community Expert
Community Expert
November 5, 2017

I opened a jpeg and tried it on my Export and the sizes do not inflate 3x like I am seeing with yours. Something is clearly wrong.

How does File > Save As > Jpeg do? By checking Preview I can see how the file size varies with the slider.

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